This invention relates to pads or blocks of sheet material, such as pads or blocks of paper. These may be pads of the kind having a flat surface defined by a straight edge of the sheets, these straight edges being stuck together so that this flat surface defines a hinge or spine of the pad. In the case of a writing pad or notepad, for example, the sheets may be detached one at a time by tearing them off from the hinge or spine surface. In the case of other forms of pads or blocks, the sheets may be intended to be permanently stuck together so that they form leaves or pages in the manner of a book. Any such form of pad or block will be referred to as `a pad of the kind specified.`
It is sometimes desirable to provide visible matter on at least one side surface of a pad of the kind specified. The side surface may be the hinge or spine surface, or it may be any side surface of the pad defined by an edge of each of the sheets which constitute the pad. Such visible matter may be decorative or may have a utilitarian or functional purpose. For example, it may be desirable to provide a notepad having on one or more of its side surfaces visible matter in the form of advertising material or the like.
It is known to make a pad of the kind specified which carries visible matter on at least one of its side surfaces by applying the visible matter to the pad by a silk screen printing process. However, difficulties sometimes arise in applying the visible matter by a silk screen printing process, particularly where it is necessary to make more than one application of visible matter to the side surface, e.g., in the case of multi-color printing. One such difficulty is in securing sufficiently accurate registration of the successive silk screens to ensure a high quality print time after time in a repetition process. One cause of this difficulty, particularly in the case of a thick pad consisting of a large number of sheets, is that it may not be feasible to clamp the pad sufficiently tightly to ensure that there is no relative movement between any of the sheets during the successive stages of the printing process.
The present invention provides an improved method of applying visible matter to a side surface of a pad of the kind specified. The advantages of the invention are particularly manifest where multi-color visible matter is to be applied to one or more of the side surfaces of a thick pad.